Multilayer stacks of polymers and oxides are deposited in a single pass coating process on flexible plastic films to make high barrier films resistant to moisture permeation. Examples of these barrier films are described in U.S. Pat. Nos. 5,440,446; 5,877,895; and 6,010,751, all of which are incorporated herein by reference as if fully set forth. These high barrier films have a number of applications in the display, lighting, and solar markets as flexible replacements for glass encapsulating materials. However, under certain conditions multilayer stacks of polymers and oxides may suffer degradation in adhesion performance after extended exposure to moisture, possibly causing these high barrier stacks to delaminate at the oxide-polymer interface and causing the flexible plastic film to detach from the device.
One solution to this problem is to use what is referred to as a “tie” layer of particular elements such chromium, zirconium, titanium, silicon and the like, which are often sputter deposited as a mono- or thin-layer of the material either as the element or in the presence of small amount of oxygen. The tie layer element can then form chemical bonds to both the substrate layer, an oxide, and the capping layer, a polymer.
Tie layers are generally used in the vacuum coating industry to achieve adhesion between layers of differing materials. The process used to deposit the layers often requires fine tuning to achieve the right layer concentration of tie layer atoms. The deposition can be affected by slight variations in the vacuum coating process such as fluctuation in vacuum pressure, out-gassing, and cross contamination from other processes resulting in variation of adhesion levels in the product. In addition, tie layers often do not retain their initial adhesion levels after exposure to water vapor. A more robust solution for adhesion improvement in barrier films is desirable.